Trouble replicating results on agent_visualizer.ipynb on colab

Hi,

I am trying to replicate the results by running the colab notebook

https://colab.research.google.com/github/google/dopamine/blob/master/dopamine/colab/agent_visualizer.ipynb

I have modified the following in order to run the code:
1. uninstalled `tensorflow 2.x` and installed `tensorflow 1.15`
2. added the argument `use_legacy_checkpoint=False` in the function `example_viz_lib.run()`

The graph for reward is generated correctly, but not the graph for the reward distribution:

The log after running `example_viz_lib.run()` is [here](https://github.com/google/dopamine/files/4833242/log.txt).

Could you please take a look and let me know what the issue is?